Thermographically color-developable composition

ABSTRACT

THERMOGRAPHICALLY COLOR-DEVELOPABLE COMPOSITIONS FOR USE IN THE PREPARATION OF HEAT-SENSITIVE COPY SHEETS AND HEAT-SENSITIVE STENCIL SHEETS CONTAINING FERROUS OR FERRIC SALTS OF HIGHER ALIPHATIC CARBOXYLIC ACIDS AND AT LEAST ONE SELECTED SEMICARBAZIDE DERIVATIVE.

United States Patent 111:. ct B41m 5700; G03(! 1/64 U.S. Cl. 117-363 Claims ABSTRACT OF THE DISCLOSURE Thermographically color-developable compositions for use in the preparation of heat-sensitive copy sheets and heat-sensitive stencil sheets containing ferrous or ferric salts of higher aliphatic carboxylic acids and at least one selected semicarbazide derivative.

BACKGROUND OF THE INVENTION This invention relates to thermographically color-developable compositions useful in the preparation of heatsensitive copy sheets and heat-sensitive stencil sheets. The term heat-sensitive copy sheets as used herein refers to sheets coated with a composition which will develop a visible image corresponding to an original when exposed to the original in a manner to be described hereinafter.

The term heat-sensitive stencil sheets refers to porous substrates coated with a heat-shrinkable thermoplastic film containing or in contact with a heat-sensitive color-developable composition, or such a porous substrate impregnated with an ink permeable resin. Stencil sheets are employed in the preparation of stencils such as are utilized in mimeographic printing.

Typical heat-sensitive copy sheets comprise a thin paper or plastic support provided with a thermographically colordevelopable layer formed by coating the substrate with a composition containing at least two compounds capable of reacting at elevated temperature to form a colored product. Typical heat-sensitive stencil sheets are prepared by aflixing a thermoplastic film to a porous thin support or impregnating the support with an ink permeable composition. The method of preparing copy sheets and stencil sheets utilizing the compositions of this invention will be described in more detail hereinafter.

The procedures for forming images on copy sheets or forming stencils from stencil sheets are well known and need not be discussed.

While a variety of heat-developable compositions are known and used in the art, none of them are completely satisfactory. Accordingly, there has been considerable effort expended in seeking new compositions which do not suffer the shortcomings of the prior art.

SUMMARY OF THE INVENTION The thermographically color-developable compositions according to the present invention are prepared to contain:

(1) At least one iron salt which is a ferrous or ferric salt of a higher aliphatic carboxylic acid having at least 10 carbon atoms; and

(2) At least one semicarbazide derivative having the formula wherein R is hydrogen, an alkyl radical preferably containing from about 1 to 10 carbon atoms, an aryl radical Patented Sept. 5, 1972 preferably containing from about 6 to 12 carbon atoms, hydroxy or an alkoxy radical preferably containing from about 1 to '6 carbon atoms, anilino or amino radicals; and A is hydrogen, alkyl or aryl radicals such as described in connection with R which together with the C=O group to which it is attached forms acyl or aroyl radicals containing from about 1 to 20 carbon atoms, anilino or amino radicals.

Typical alkyl radicals include straight and branch chain radicals such as methyl, decyl, isopropyl, t-butyl, and the like. Typical aryl radicals include phenyl, tolyl, xylyl, biphenyl, naphthyl and similar radicals. Acyl radicals may suitably be selected from formyl, acetyl, propionyl, butyryl, valeryl, palmitoyl, stearoyl, oleoyl, oxalyl, malonyl, succinyl, benzoyl, toluoyl, salicyloyl, cinnamoyl, naphthoyl, phthaloyl, or furoyl.

The iron salts are ferrous or ferric salts of higher aliphatic carboxylic acids. The preferred salts are derived from saturated and unsaturated acids containing from about 10 to 25 carbon atoms. Salts with a smaller number of carbon atoms while useful are generally not practical because of their offensive odor. Salts with more than 25 carbon atoms may similarly be employed but are generally not preferred since they are difficult to synthesize or to purchase commercially.

Thiosemicarbazide derivatives have been similarly employed in the prior art. However, the semicarbazidcs utilized herein have a number of most unexpected advantages when compared to the prior art sulfur analogs. Perhaps the most significant advantage of the compositions of this invention is that their ability to form colored derivatives does not deteriorate with storage as is the case with compositions based on thiosemicarbazides.

The semicarbazide derivatives utilized in the practice of this invention are all known or can be prepared by known methods. Typical processes are illustrated in the examples.

Ferrous and ferric salts of the saturated and unsaturated aliphatic carboxylic acids employed in the invention are readily prepared by reacting the selected soluble iron salt in an aqueous media with the acid. Iron salts of the following acids are typical of those which may be used: nundecyclic, lauric, myristic, palmitic, margaric, stearic, arachidic, behenic, lignoceric, oleic and linoleic.

As will be apparent from the descriptions hereinafter the semicarbazide derivative and iron salt utilized in this invention may appear in a variety of both wet and dry media. They may be dissolved or dispersed, for example, in a liquid vehicle or dispersed in a solid. The liquid may be simply one which serves as a vehicle by which the reactants are spread onto the substrate. It may be one which additionally contains a resinous substance serving as an adhesive or as the thermoplastic film to be perforated in the conversion of a stencil sheet to a stencil. The solid vehicle may be the dried adhesive on the substrate or it may be the plastic film of a stencil sheet or a. copy sheet. 'It is possible that one reactant may be in a first liquid vehicle and the other reactant in a second liquid vehicle and that the two are not brought into reactive proximity until they are spread on the support. In any event, the vehicle whether solid or liquid is inert with respect to the reaction which takes place between the semicarbazide derivative and the iron salt. For convenience the vehicle will be referred to herein as an inert carrier.

The weight ratio of iron salt of higher aliphatic carboxylic acid to semicarbazide derivative in an inert carrier with both copy sheets and stencil sheets is from about 1:0.1-2. The preferred ratio, especially for the preparation of stencil sheets, is 1:0.1-0.3. The weight of reactants on the substrate in copy sheets is from about 0.1-5 g./m. and the optimum amount is about 2 g./m. For

the preparation of stencil sheets the amount of reactants is from about 0.13 g./m.

The reaction by which the colored product is formed is effected at approximately the temperature at which either or both of the reactants melt. The colored products which form the images therefore normally are produced at a temperature of from about 50 C.-150 C.

Utilizing the compositions of this invention it is possible to prepare copy sheets which are inexpensive, do not develop a cloudy appearance on storage and are substantially free from deterioration of color-developability during storage. The reactants can be selected to produce black, blue or brown color in striking contrast to the background support even though they are employed in small amounts.

In the presently preferred process an iron salt of an aliphatic carboxylic acid and the semicarbzaide derivative are slowly mixed in a liquid carrier to form a solution or suspension which is then coated by any convenient method onto a substrate such as standard paper, parchment paper, sulfate paper, cellophane, or the like or a synthetic resin film, for example, cellulose acetate or polyethylene terephthalate, or on resin impregnated paper or cloth. The carrier by means of which the reactants are bonded to the substrate may be any of a variety of such carriers normally employed with the prior art compositions and include, for example, ethyl cellulose, methyl cellulose, cellulose acetate and other cellulose derivatives, polyvinyl acetate and copolymers thereof, polyvinyl chloride and copolymers thereof, polyvinyl alcohol, polyvinyl butyral, polyamides, polystyrene and copolymers thereof, silicon resins, resins based on phenol and synthetic materials.

The image is formed on the copy sheet by any of the usual procedures. For example, the original is brought into contact with the copy sheet either on the side carrying the heat-sensitive materials or on the opposite side and the image is developed on the copy sheet by the application of infrared rays in accordance with standard practice.

The image formed on the copy sheets of this invention is extremely stable especially at room temperature and does not discolor or fade appreciably when exposed to sun light. As a result no fixing step is required for the production of a permanent image.

Heat-sensitive stencil sheets may be divided broadly into two categories. These are:

(a) Stencil sheets prepared by afiixing a thermoplastic film, for example, a copolymer of vinyl and vinylidene chloride, which is about 7 thick to a thin porous support such as paper; and

(b) Stencil sheets prepared by impregnating a thin porous material such as paper with an ink-permeable agent suitably a cellulose derivative such as ethyl cellulose, cellulose acetate-butyrate or cellulose acetate-propionate, polystyrene and copolymers thereof, polyvinyl chloride and copolymers thereof, polyacrylic and polymethacrylic esters and wood resin.

There are four principal methods by which stencil sheets of class (a) above are formed in accordance with this invention. These are:

(l) The reactants are dispersed or dissolved in a bonding or adhesive agent which is coated onto a substrate and thereafter coated with a thermoplastic film.

(2) Either the iron salt of the carboxylic acid or the semicarbazide derivative is dispersed or dissolved in the bonding agent which is applied to the substrate and the other reactant is coated onto the thermoplastic film which is bonded to the substrate.

(3) Both reactants are dissolved in a volatile solvent which is coated onto the thermoplastic film.

(4) Either of the reactants is mixed into pellets for use in formation of the thermoplastic film and the other reactant is dispersed or dissolved in the bonding agent used to bond the film to the substrate.

One method of forming stencil sheets of class (b) above is to disperse or dissolve both reactants into the same solvent which contains the ink-permeable layer forming agent before impregnation of the porous substrate. Another is to impregnate the porous substrate in the usual way and thereafter apply the reactants to the surface of the substrate in a liquid carrier which is then dried.

The porous substrate for use in the preparation of sten cil sheets of class (b) above may be any of those generally employed for such purposes including paper, woven or non-woven fabrics, finely meshed screen and the like.

The processes above described are further illustrated in the examples.

In practice the colored products formed at elevated temperatures concentrate along the edges of the perforated portion of the thermoplastic film of the stencil and also adhere to the porous support so that it becomes possible to visually estimate the suitability of the stencil sheet for use in printing.

The thermographically color-developable compositions of this invention are capable of developing highly colored images even when employed in small amounts. This is particularly important in connection with the production of stencils which otherwise would have poor resolving power.

The stability of the compositions of the invention is often improved by the presence of a small amount of stabilizing agent which may be an acid or a salt of an acid. Normally from about 0.005-0.3 part by Weight of stabilizing agent per one part by weight of the composition is effective. Suitable stabilizing agents include inorganic acids such as sulfuric, hydrochloric, nitric, or phosphoric; or organic acids such as lauric, myristic, palmitic, stearic, erucic, behenic, abietic, naphthenic, oxalic, malonic, succinic, malic, tartaric, citric, maleic, cyanoacetic, benzoyl acetic, or benzoic. Ammonium or metallic salts of these acids especially sodium, potassium, zinc, lead and cadmium salts are also effective.

The following non-limiting examples are given by way of illustration only.

EXAMPLE 1 Synthesis of semicarbazide derivative.--A solution was first prepared by dissolving 190 g. of methyl isocyanate into 250 ml. of ethanol. Subsequently, another solution prepared by mixing 230 g. of hydrazine hydrate of purity in 250 ml. of ethanol was slowly dropped into the former solution with continuous stirring and cooling whereby there were obtained white crystals of 4-methyl semicarbazide (having a melting point in the range of 1l61 17 C.). The crystals were then recrystallized from ethanol and dried. 108 g. of thus obtained 4-methyl semicarbazide was mixed with 167 g. of formic acid and 111 ml. of normal propanol, refluxed and cooled. The resultant white precipitate was recrystallized from ethanol, and there was obtained 1-formyl-4-methyl semicarbazide having a melting point in the range of 236238 C.

Preparation of heat-sensitive copying material.20 g. of the powder obtained through the foregoing method was mixed in ml. of a 5%-toluene solution of a silicon resin and subjected to dispersion by means of a ball-mill for 5 hours, to form a suspension. Another suspension was prepared by mixing 30 g. of a ferrous salt of lauric acid and 100 ml. of 5% toluene solution of silicon resin for 8 hours on a ball mill. The two suspensions were mixed and the resultant mixture was coated onto a tracing paper to the extent of about 5,41. in thickness and dried in a cold air current to prepare a heat-sensitive copying material. This copying material, when utilized for copying by employing a thermographically copying machine (Thermofax manufactured by Minnesota Mining & Manufacturing Company), produced a clear-cut image formed in brown color on a snow-White ground. The poststorage stability of the copy thus produced proved to be exceptionally good.

Example 2 Synthesis of semicarbazide derivative-Utilizing phenyl isocyanate in lieu of methyl isocyanate used in case of Example 1 and employing a similar process, l-formyl-4- phenyl semicarbazide (having a melting point in the range of l72173 C.) was produced.

Preparation of heat-sensitive stencil sheet.By employing a mixture prepared by mixing 5 g. of the powder obtained through the foregoing method, 5 g. of a ferric salt of stearic acid (having a melting point in the range of 103 106 C.) and 1 g. of stearic acid as a stabilizer in 1300 ml. of 6%-methanol solution of polyvinyl acetate, and effecting thorough dispersion by means of a ball-mill for 24 hours, a bonding agent containing the thermographically color-developable composition was prepared. Subsequently, a plastic film comprising 7 .-thick transparent vinylidene chloride-vinyl chloride copolymer as its principal component and a porous thin paper comprising manila hemp fiber as its principal component and weighing 9 g./m.= were affixed together by means of said bonding agent. An original carrying the desired image printed thereon was superposed onto the film-side of thus obtained stencil sheet, and infrared rays were applied by way of the thin-paper side by employing the same thermographic copying machine employed in Example 1, to eifect perforation of the film. At the time of preparing the stencil, the extent of exposure was varied. A number of stencils were prepared. Those having a blue colored image on the perforated area well contrasted with the White background were used to produce prints of exceptional quality.

Example 3 50 g. of cellulose-acetate-butyrate (namely, Half Second Butyrate manufactured by Eastman Chemical Co.) was dissolved in 500 ml. of acetone, and a solution thus obtained was mixed with 100 g. of hydrogenated abietic acid ester (a manufacture of Hercules Powder Co., USA, with the brand name Hercolin D) and 50 g. of a mineral oil having the aniline point of 97 C. The mixture thus obtained is hereinafter referred to as Solution A.

Subsequently, 1 mole of phenyl isocyanate was mixed with 500 ml. of methanol at room temperature, and into a mixture thus prepared was dropped a solution prepared by mixing 2 mols of hydrazine hydrate in one liter of methanol. A white powder was obtained which wa recrystallized from glacial acetic acid to produce hydrazine dicarbonanilide having a melting point of 245 C. The thus obtained powder g.) was added to 200 ml. of acetone, and dispersed using a ball-mill for 7 hours. The disperson thus prepared is hereinafter referred to as Solution B. A total of 30 g. of the ferrous salt of palmitic acid was added to 300 ml. of acetone and dispersed in a ball-mill for 20 hours. This dispersion is hereinafter referred to as Solution. C.

A blended solution was prepared by mixing the foregoing Solutions A, B and C and it was coated and impregnated on and in a porous thin paper weighing about 10 g./m. so that the post-drying weight of the substance thus adhered to the thin paper be about g./m. When the heat-sensitive stencil sheet thus prepared was subjected to processing utilizing the Thermofax machine, the stencil obtained by proper exposure was provided with an image having a green color well contrasted with the white background and formed only on the perforated area thereof.

Employment of said stencil for printing by a rotary press resulted in a large number of clear-cut prints faithfully repoducing the original image.

Example 4 Acetyl semicarbazide was prepared according to the procedure of Beilstein Organische Chemie, 1929, vol. III/IV p. 56, and 5 g. of the compound was taken up in 100 ml. of methanol. A mixture thus obtained is here inafter referred to as the Component A.

6 Next, 15 g. of ferric caprylate and l g. of sodium caprylate were mixed in 100 ml. of 2%-methanol solution of vinyl acetate-methyl methacrylate copolymer and dispersed therein utilizing a ball-mill for 24 hours. This dispersion is hereinafter referred to as the Component B.

Example 5 125 g. of benzazide and 100 g. of acetone-acetyl hydrazone were dissolved in anhydrous pure acetone and refluxed for 10 hours. The acetone was evaporated and lacetyl-4-phenyl semicarbazide was deposited from the boiled water (see Beilstein, 1910, vol. 7, p. 383).

The thus obtained compound (20 g.) was dissolved in 100 ml. of l0%-methanol solution of ethyl cellulose. This solution is hereinafter referred to as the Component A.

Next, 20 g. of ferrous stearate, 3 g. of stearic acid and 20 g. of talc (slip-resisting agent) were mixed in 500 ml. of methanol and dispersed utilizing a ball-mill for 20 hours. The dispersion thus prepared is hereinafter referred to as the Component B.

Subsequently, by means of applying a coating liquid for use 1n conventional art-paper processing (viz. a solution prepared by dispersing clay in an aqueous solution of polyvinyl alcohol) on a smooth paper weighing g./m. and drying thereafter, a supporting sheet was prepared. Then, equivalent amounts of the aforesaid Components A and B were thoroughly mixed with each other and applied on the coating layer of the supporting sheet, and dried by employing a warm air current having a temperature not exceeding 50 C. The dry weight of thus coated heat-sensitive layer was 5 g./m.

When thus prepared heat-sensitive sheet was heated by means of a thermal printer such as is described in US. Pat. No. 3,496,333 very distinct characters consisting of blue-black points on the white texture of the sheet were produced.

When a conventional heat-sensitive copy sheet was compared with the heat-sensitive sheet of this example the former developed the coloring in 0.1 second at a temperature of 110 C. while the latter could develop color to a satisfactory degree in 0.1 second at a temperature of C. This illustrates a particular advantage of the heat-sensitive sheets of this invention. It is sufiicient to utilize a thermal printer having a lower temperature than is conventionally employed.

Example 6 After fusing semicarbazide and anhydrous benzoic acid, and recrystallizing from water there was obtained 1- benzoyl-semicarbazide (see Beilstein, 1910, vol. 9, p. 327).

The thus obtained compound (20 g.) and 2 g. of sodiurn erucate were dissolved in 500 ml. of water. This solution is hereinafter refererd to as Component A.

15 g. of ferric erucate and 5 g. of erucic acid were mixed with 500 ml. of a 5% aqueous solution of polyvinyl alcohol and dispersed utilizing a ball-mill for 30 hours. This dispersion is hereinafter referred to as the Component B.

Subsequently equal amounts of Components A and B were blended, applied onto a tracing paper, and dried. The tracing paper was then treated as in Example 1. As a result, there was obtained a copied image in dark-brown color on a light brown texture.

Example 7 130 g. of hydrogen sulfate and 136 g. of crystalline sodium acetate were dissolved in 1300 ml. of water, and the solution was cooled and mixed with potassium cyanate. Thus treated solution was maintained weakly acidic with acetic acid and, 2 hours later, it was additionally mixed with 25 to 30 g. of potassium cyanate and left standing overnight to produce hydrodicarbonamide (see Beilstein, 192l,vol. 3,p. 116).

g. of this compound and 1 g. of sodium behenate were mixed in one liter of methanol. This solution is hereinafter referred to as Component A.

g. of ferric behenate, 6 g. of behenic acid, and 10 g. of talc were added to 500 ml. of a 3% solution of methyl cellulose and dispersed therein by mixing in a ball-mill for 10 hours. This dispersion is hereinafter referred to as Component B.

Subsequently equal quantities of Components A and B were thoroughly blended and applied to the extent of 15 g./m. dry weight on an art-paper weighing 100 g./m. The coating was dried by employing a warm air current having a temperature not exceeding 50 C.

The heat sensitive sheet was utilized as in Example 5. There was obtained a black-colored copied image which was clear against the light brown texture.

What is claimed is:

1. A thermographicaly color-developable composition comprising an inert carrier containing (a) at least one iron salt which is a ferrous or ferric salt of a higher aliphatic carboxylic acid having at least 10 carbon atoms; and

(b) at least one semicarbazide derivative having the formula wherein R is hydrogen, an alkyl radical containing from about 1 to 10 carbon atoms, an aryl radical containing from about 6 to 12 carbon atoms, hydroxy or an alkoxy radical containing from Cit about 1 to 6 carbon atoms, anilino or amino radicals;and

A is hydrogen, an alkyl or aryl radical which together with the 0:0 group to which it is attached forms an acyl or aroyl radical containing from about 1 to 20 carbon atoms, anilino or amino.

2. A composition as in claim 1 wherein the ratio of iron salt to semicarbazide derivative is about 1:0.1-2.0.

3. A composition as in claim 1 stabilized by the addition of an effective amount of an acid, an ammonium salt of an acid or a metal salt of an acid.

4. A copy sheet coated with a composition of claim 1.

5. A stencil sheet coated or impregnated with a composition of claim 1.

6. A composition of claim 1 wherein the semicarbazide derivative is 1-formyl-4-methyl semicarbazide and the iron salt is ferrous laurate.

7. A composition as in claim 1 wherein the semi-carbazide deriative is 1-formyl-4-phenyl semicarbazide and the iron salt is ferric stearate.

8. A composition as in claim 1 wherein the semi-carbazide derivative is hydrazine dicarbonanilide and the iron salt is ferrous palmitate.

9. A composition as in claim 1 wherein the semi-carbazide derivative is acetyl semicarbazide and the iron salt is ferric caprylate.

10. A composition as in claim 1 wherein the semicarbazide derivative is l-acetyl-4-phenyl semic'arbazide and the iron salt is ferric stearate.

References Cited UNITED STATES PATENTS 2,739,893 3/1956 Levy 961l4.5 2,999,035 9/1956 Sahler 1l7-36.8

NORMAN G. TORCHIN, Primary Examiner A. T. SURO PICO, Assistant Examiner US. Cl. X.R. 96-92 

